1. Field of the Invention
This invention relates to contiguous filterbanks using surface acoustic wave (SAW) technology and, in particular, to filterbanks that produce an output signal with amplitude and phase characteristics to provide a continuous response across the entire bandwidth of the filterbank. These filterbanks can provide a range of bandwidth varying in discrete steps and are sometimes referred to as bandwidth switchable SAW filters (BSSF).
2. Description of the Prior Art
It is known to have filterbanks containing filters containing surface acoustic wave technology. Theoretically, a filterbank should produce an overall result that is the sum of the results of the individual filters. In most applications of filterbanks, it is desirable that the sum of these results should overlap sufficiently so that the combined response of the filters is continuous across the combined bandwidth. In practice, with known filterbanks, the theoretical response was not achievable and the combined response was not continuous across the combined bandwidth or the amplitude and phase characteristics of all filters do not track closely over the operating temperature range. The individual filters of the filterbank for BSSF filters often require a wide difference of bandwidths among the individual filters. The requirement for dissimilar bandwidths conflicts with that for identical tracking and theoretical responses have not been previously obtainable in practice. Further, with dissimilar bandwidths, substantial amplitude and phase offsets may occur over temperature.